I’ve never understood why so many people fawn over Hawking or think that he is so smart. My guess is that the guy who “interprets’ his grunts and groans is the “brains” and Hawking is the Charley McCarthy of the duo. If Hawking said this, then it proves that theory.
Hawking's disease and the way he presents himself to the world -- in that wheelchair and communicating only by tapping on a button, makes him a more mythical character and adds to the drama. That's why he is taken so seriously.
Now if I were really cynical I would say it's all part of an elaborate hoax to market Hawking and his "ideas". But I am not, so I won't.